Any discussion of the background art throughout the specification should in no way be considered as an admission that such art is widely known or forms part of common general knowledge in the field.
Optical or photonic switches are central components in optical networks and provide routing of optical signals from a source to a destination in the purely optical domain. Optical switches can be divided broadly into two main categories: wavelength selective switches and wavelength independent switches.
Wavelength selective switches provide capability for switching specific wavelength channels within wavelength division multiplexed (WDM) signals and are generally more complex and expensive devices. A specific type of wavelength selective switch is a Reconfigurable Optical Add-Drop Multiplexer (ROADM), which is capable of multiplexing and demultiplexing a WDM signal to dynamically add or drop particular wavelength channels.
U.S. Pat. No. 6,718,082 to Zhao and Lin, entitled “Solid-State optical wavelength switches” discloses a solid-state polarization-rotation based optical switch that has wavelength selective functionality. Wavelength selectivity is achieved by passing light through a birefringent crystal filter, which selectively rotates the polarization of one wavelength of light by 90° with respect to another wavelength, thereby providing separate routing of the wavelengths. Zhao and Lin is a passive type switch wherein the beams are split and routed to the output ports without active switching to select a specific output port. Further, Zhao and Lin is limited to a 1×2 type switch.
Another known types of wavelength selective switch include those disclosed in U.S. Patent Application Publication US 2009/0180779 A1 to Boduch and Papakos, entitled “Methods and apparatus for performing directionless wavelength addition and subtraction within a ROADM based optical node” and Maher and Deogun, “Cost-Effective Implementation of Multicasting in Wavelength-Routed Networks”, Journal of Lightwave Technology, Vol. 18, No. 12, December 2000. The former discloses a reconfigurable optical add/drop multiplexer, while the latter proposes a wavelength selective multicast type optical cross connect at an architectural level.
These and other known wavelength selective switches involve demultiplexing wavelength channels of predetermined spectral dimensions and subsequently switching those individual channels. Therefore, these types of switch are not capable of switching signals having variable or arbitrary channel plans.
Wavelength independent switches, on the other hand, provide more flexible routing of optical signals between nodes of a network where knowledge of individual channel spectral dimensions is not required. For example, where groups of channels are concurrently routed. US Patent Application Publication 2011/0164876 A1 to Fujita et al. entitled “Directionless Reconfigurable Optical Add/Drop Multiplexer” (assigned to Enablence USA Technologies Inc.) discloses an N×M optical switch system including a generic optical splitter coupled to each of the N input fibers for splitting each of the N input signals into M or fewer sub signals. The M sub signals are received by M generic optical N×1 switches, which are each capable of selecting one of the N input signals for output. In the case of multiplexed input signals, the signals output from the switches are passed through filters to produce demultiplexed, single-wavelength output signals.
While Fujita et al. discloses a general architecture for providing N×M switching, it is cast at a functional level and does not provide component level implementation details. As such, important factors such as polarization independence, switching extinction, manufacturing complexity and cost are not considered. Further, Fujita et al. require the components to be “optically connected”. In the illustrated architectures, components such as optical filters, amplifiers and the like are included, which would likely limit the optical connections to physical waveguides such as optical fibers. This restriction, which is common to many wavelength selective and wavelength independent designs, has particular performance drawbacks and requires each input fiber to have a corresponding beam splitter and individual N×1 optical switches.
Therefore, there is a general desire for low cost non-complex optical switches.